Bond Prices and Interest Rates

Yesterday I posted a piece about inflation and interest rates arguing that although recent inflation numbers have been very tame, the tsunami of bank reserves (=800%) released by the Fed is beginning to show up in inflation expectations, which is why long Treasury yields are rising. I ended with a warning that long-term bonds, not stocks, are the riskiest assets in our portfolios today.

A good friend asked me to review some of the logic in more detail. I will do so below:

1) The link between rising interest rates is not just a theory that might or might not be true. It is the definition of an interest rate, or yield.

For example, In the chart below, if you pay pay $95.24 to buy a bond (really just an IOU) that promises to pay you $100 in one year then we would calculate its yield as r = ($100-$95.24)/$95.24 = $4.76/$95.24 = 5.0%.

If something changes in the marketplace and people lose interest in owning bonds so that their price falls to $90.91 then we would calculate their yield to be r = ($100-$90.91)/$90.91 = $9.09/$90.91 = 10.0%.

SO, SAYING THAT INTEREST RATES GO UP FROM 5% TO 10% IS THE SAME EXACT STATEMENT AS SAYING THAT BOND PRICES ARE FALLING.

2) the interest rate, or yield, (which is just a calculation we make by dividing a contractual interest payment by the price we pay for the security) on all sorts of securities rises and falls with inflation (actually expected inflation. Bet way to understand this is to think of the inflation rate as the “interest” you receive from owning a tangible asset like a house or a bar of gold. If you buy it for $100 this year and its prices goes up to $110 in one year (10% inflation) then the “yield” on the asset is $10/$100 = 10% (the increase in value divided by what you paid.)

The logic is; inflation goes up => “yield” on real goods goes up => that makes the yield on real goods high compared with the yield on bonds and other securities => that makes people sell bonds to buy more houses and other hard assets => that pushes hard asset prices up and bond prices down => Falling bond prices increases the yield. => SO YOU DON’T WANT TO OWN BONDS WHEN THEIR PRICES ARE FALLING.

3) Over long periods the price level will be roughly proportional to the money supply. The money supply is roughly proportional to bank reserves. The Fed has increased bank reserves by +800% since last September. Together these mean that there is a big increase in the price level, hence inflation, baked into the recent Fed policy. When the economy starts to look a little more normal again (it is starting to do this already) people are going to worry about inflation unless the Fed does something to reverse their actions over the past 6 months.

Moral of the story–you don’t want to own bonds when people start worrying that inflation, hence interest rates, will go up.